As a device for a computer to effectively store information required for computing, a storage system is well known. By connecting one or more computers and one or more storage systems to SAN (Storage Area Network), the computer can store information in the storage system.
A storage system is a system including one or more auxiliary storages capable of storing information of HDDs (Hard Disk Drives), SSDs (Solid States Drives) and others permanently which, following information read/write requests from the computer, reads or writes information from or to the auxiliary storages and returns the result to the computer. Furthermore, when reading or writing information from or to the auxiliary storage, the storage system performs the RAID (Redundant Arrays of Independent (or Inexpensive) Disks) processing. RAID is the technology of using multiple storages as one storage for the purpose of improving the reliability and, for the prevention of information loss in case of failure in part of the storage system configuring RAID, of storing information for recovery (parity) in multiple storages. A group of storages that configure RAID is called an RG (RAID group). An area divided into one or more of a storage area of an RG is called a logical volume. The computer requires the logical volume to read or write information.
It is well known that the power consumption of the storage system can be estimated with reference to the access frequency to the RG or the operation rate of HDDs. The access frequency is the number of information read/write requests (I/O requests) to the RG per unit of time. The HDD operation rate is the percentage of the length of time taken since the HDD receives a read or write request till it returns the response in a unit of time.
Meanwhile, according to the Patent Citation 1, the storage system can provide the computer with a virtual logical volume realized by a technology called thin provisioning. A virtual logical volume is similar to a logical volume in that it is an area to store information. However, a virtual logical volume is different from a normal logical volume as, when an information write request is transmitted to a virtual logical volume, a required area in a group of logical volumes called a pool is allocated to the virtual logical volume to which the information write request is transmitted. If an information write request is transmitted to an area to which a virtual logical volume has already been allocated, information is written to the already allocated area. If a request for reading information is transmitted to an area to which a virtual logical volume has already been allocated, information of the already allocated area is returned. If an information read request is transmitted to an area to which no virtual logical volume is allocated, empty information is returned. Since a required number of areas is allocated at the required time by using virtual logical volumes, the utilization efficiency of the auxiliary storage device is improved. Furthermore, the total capacity of logical volumes belonging to a pool can be reduced to be smaller than the total capacity of virtual logical volumes belonging to the same pool.